A study released by the British Medical Journal found that people tend to pour 20-30% more alcohol into short, wide 350ml glasses than into tall, narrow 350ml glasses. The researchers go on to state that alcohol consumption studies should also include the shape of the glass.
The reason for the difference, Wansink speculates, is the classic vertical-horizontal optical illusion: People consistently perceive equally sized vertical lines as longer than horizontal ones.
“People generally estimate tall glasses as holding more liquid than wide ones of the same volume,” Wansink said. “They also focus their pouring attention on the height of the liquid they are pouring and insufficiently compensate for its width.”
It’s a good thing we have bowl shaped glasses for wine as this study shouldn’t pose to much of a problem for wine drinkers worried about getting their money’s worth in the tasting room.
But there are other factors that can effect fair pouring when wine tasting. Most likely mood, prejudice, likes, dislikes, stress, glass thickness, time of day, etc., can alter the amount poured. Mechanical pouring devices offer a solution to this, but they still aren’t used at every winery.
The real solution is to bring your own glass when tasting.